J. Phys. Ther. Sci. 10: 47Ð51, 1998 The effects of on Standing Posture Control

MASATAKA HOSODA1), OSAMU YOSHIMURA2), KIYOMI TAKAYANAGI2), RYUJI KOBAYASHI1), AKIRA MINEMATSU1), HISATO SASAKI1), HIROSHI MAEJIMA1), YUITI MATSUDA1), SHIHO ARAKI2), AKIKAZU NAKAYAMA3), TOSHIRO ISHIBASHI3), TAKASHI TERAZONO4)

1) Hiroshima University Graduate School of Medicine, 1Ð2Ð3 Kasumi, Minami-ku, Hiroshima City, Hiroshima 734-0037, . TEL +81 82-257-5430. 2) Institute of Health Sciences, Hiroshima University School of Medicine 3) Kyushu College of Rehabilitation 4) Ishii Cure Clinic

Abstract. Influences on dynamic balance were examined by comparing footwear with thongs such as with clog thongs, to footwear without them such as slippers without clog thongs, leather-soled , and Japanese . Forty three university students in good health took part in this examination. In the case of footwear with clog thongs, postural response latencies to horizontal movement of the platform were decreased when compared with that for slippers without clog thongs. In the case of footwear with clog thongs, standing strength was decreased when the platform moved horizontally, compared with that for slippers without clog thongs. Among footwear with clog thongs, in the case of Japanese socks, both latency and strength were minimal compared to slippers with clog thongs and leather-soled sandals. Therefore, it can be said that footwear with thin soles, low heels and clog thongs the most stable and the best for preventing a fall. Key words: Standing pusture control, Dynamic balance, Equitest.

(This article was submitted Mar. 16, 1998, and was accepted May 20, 1998)

balance function. However, in daily life, postural INTRODUCTION control is required in response to change in situa- tions such as speed change on a train, unexpected When human beings stand, only their feet di- change of surface while walking and so on. It has rectly touch the ground. They are unique in terms been reported that elder people fall down when of adjustment of posture because they have they are exposed to unexpected and accelerated bipedality. perturbations such as tumble and slip. In consider- The feet, in their functions as sense organs and ing daily human activities, it is important to receptors, play a key role in the maintenance of evaluate the dynamic balance of each action. Most standing posture. As sense organs, the feet support existing studies concerning dynamic balance have the body and adjust the center of pressure in order to lacked objectivity, repeatability and depth. How- prevent falls. As receptors, they collect information ever, improvements in test machinery, data through the skin of the sole, muscle, and tendons, processing ability and peripheral equipment result- making smooth adjustment of posture possible. So ing from advances in technologies make it easier to far a lot of studies have been done regarding static examine dynamic balance even in a clinical study. balance in standing postural control and this re- Recently, in Japan’s increasingly aging society, search has been applied to the evaluation of the the issue of violent falls of the elderly has been 48 J. Phys. Ther. Sci. Vol. 10, No. 1, 1998 focused on and interest in the balance function has been growing. There have been remarkable im- provements in the surgical technology of fractures of the cervix, thighbones and so on and these have greatly contributed to people’s quality of life. On the other hand, how to prevent falls and minimize fall damage have been comparatively neglected. Measures to prevent falls include maintenance of the balance function, development of protectors and shock-absorbing pads for thighbones, new types of footwear designed to prevent falls, and environmental features of buildings. This study examines more closely fall prevention and postural control and focuses on footwear with clog thongs which are one of the best means of preventing falls in terms of footwear. It aims to quantitatively ex- amine dynamic standing balance and discuss the effects on standing postural control.

SUBJECTS

The subjects were 43 healthy university students (female 33, male 10), aged from 18 to 23 (mean age 21.4 ± 2.7), and their mean height was 160.6 ± Fig. 1. The Equitest device is a device with a self-contained power source. 7.4 cm (147~175 cm).

METHOD matic sensation. The latter test applies various dis- In order to examine standing dynamic balance, turbances to the platform on which subjects are the Equitest system was used (Fig. 1). This gives standing and examines how quickly they are able dynamic perturbation information relating to so- to precisely adjust their posture. In this test the matic sensation as well as visual sensation by using force plate on the floor will suddenly move back a mobile platform and foreground board with com- and forth and the pole attached to both thighs will puter control. It detects perturbation of the center move forward. of gravity and the body equilibrium of subjects by The physical responses to these movements are using a pressure sensor which is installed inside analyzed, and the index parameters of the valua- the platform and sends information to a computer tion are latency and strength. Latency shows the for analysis. When the platform and the fore- period, in milliseconds, from when the platform ground board are in the leaning mode, the starts to move until subjects start to adjust their equipment detects the approximate tilt angle of postures. Strength indicates the responses, mea- subjects. Taking into account the subjects prere- sured in pounds, that subjects produce when they corded physical data and the movements in their try to maintain their balance despite the movement center of gravity determined by the pressure sen- of the platform. The types of footwear which were sor, it decides the follow-up angle. The EquiTest used in this study were 1) slippers without clog examines the results and determines two tests, the thongs (Fig. 2), 2) slippers with clog thongs (Fig. sensory organization test and the motor control test 2), 3) leather-soled sandals (Fig. 3), and 4) Japa- ( for short MCT as follows). nese socks (Fig. 3). In the cases of 1) and 2), we The former examines how to maintain favorable attempted to equalize elements such as the height balance under various sensory conditions, combin- of heels and the area which covers the forefoot, ing diminished sensory input, confusion in static except for clog thongs. The range of heel heights standing posture and control and disruption of so- were 1) 3.4 cm, 2) 3.1 cm, and 3) 0.9 cm. 49

ment time of the platform was set at 400 ms. Mea- surement was automatically carried out three times at random and the data of responses during 2.5 seconds was recorded by a computer. The distance of movement was decided using the equation “5.72 cm × height ÷ 72”, allowing personal differences to be taken into account. The average figures of results from three measurements for both lower limbs was adopted and if subjects’ feet left the platform, it was noted as “Fall” and excluded from the data. Since a normal distribution didn’t appear from the data we obtained, we adopted the Fig. 2. slippers without clog thongs (left) and slippers Wilcoxon order approval, which is non parametric, with clog thongs (right). for statistical analysis.

RESULTS

1) Latency: ms (Table 1, Table 2) In terms of latencies to the backward horizontal movement, the latency of (1) slippers without clog thongs was significantly longer than that of (2) slippers with clog thongs (p<0.0001), leather-soled sandals (p<0.0001) and (4) Japanese socks (p<0.0001). With forward movement, the latency of (1) slippers without clog thongs was also significanty longer than that of (2) (p=0.0003), (3) (p=0.0008) and (4) (p<0.0001). When results of footwear with clog thongs in backward horizontal Fig. 3. leather-soled sandals (left) and Japanese socks movement were compared, the latency of (4) Japa- (right). nese socks was significanty shorter than that of (2) slippers with clog thongs (p=0.0014), and (3) leather-soled sandals (p=0.0006). The MCT was employed as the means of mea- surement with the stimulus limited to horizontal 2) Responding strength: pound (Table 3, Table 4) back and forth perturbation. Prior to measurement, When the platform was moving horizontally the purpose and method of the study were ex- backwards, the strength of the response when wear- plained to the subjects and their consent obtained. ing (1) slippers without clog thongs was stronger Although details about the contents of the exami- than that of (2) slippers with clog thongs (p=0.0177), nation were explained to the subjects, they were (3) leather-soled sandals (p=0.0007), and (4) Japa- not permitted to practice before the test. The type nese socks (p<0.0001). In the case of forward of footwear to be worn was chosen from 1) to 4) at horizontal movement, the strength of the response random. Subjects were asked to put their feet sepa- when wearing (1) was stronger than that of (2) rately on the two boards keeping a standing (p<0.0001), (3) (<0.0001) and (4) (p<0.0001). posture, and to look carefully at the foreground When footwear with clog thongs, (2) (3) & (4), board. They were then asked to align the center of were tested in backward horizontal movement, the their leg joints with the movement axis of the plat- strength of the response when wearing (2) slippers form and to rest their arms at the sides of their with clog thongs was significanty stronger than that bodies. In order to get good postural responses, of (3) leather-soled sandals (p=0.0284) and (4) more specific instructions on stance were not Japanese socks (p<0.0001). In forward horizontal given, so that the subjects would be able to adopt a movement, the strength of the response when wear- relaxed standing posture. The horizontal move- ing (2) slippers with clog thongs was significanty 50 J. Phys. Ther. Sci. Vol. 10, No. 1, 1998

Table 1. Latency of the backward horizontal movement slippers without slippers with leather-soled Japanese socks clog thongs clog thongs sandals latency (ms) 134 ± 9 125 ± 10 126 ± 9 121 ± 9

Table 2. Latency of the forward horizontal movement slippers without slippers with leather-soled Japanese socks clog thongs clog thongs sandals latency (ms) 128 ± 9 123 ± 8 123 ± 9 119 ± 9

Table 3. Strength of the backward horizontal movement slippers without slippers with leather-soled Japanese socks clog thongs clog thongs sandals strength (pound) 9.7 ± 9 9.0 ± 3.0 8.1 ± 3.0 7.7 ± 2.3

Table 4. Strength of the forward horizontal movement slippers without slippers with leather-soled Japanese socks clog thongs clog thongs sandals strength (pound) 10.6 ± 2.8 9.4 ± 3.0 8.5 ± 2.9 7.7 ± 2.1 stronger than that of (3) leather-soled sandals is the most important mechanoreceptor among (p<0.0001) and (4) Japanese socks (p<0.0001) and other receptors on the sole of foot. It is greatly furthermore the strength of the response when developed in the area of forefoot which touches the wearing (3) leather-soled sandals was significanty ground and there is a particularly high density in stronger than that of (4) Japanese socks. the first medium-footbones. When people wear footwear which separates the big toe from the other DISCUSSION toes by means of clog thongs, the big toe and its cells will be directly stimulated. In addition, In the horizontal movement of the platform, the muscle changes in the sole will activate the input latency for slippers without clog thongs was longer fibers of joints and transmit high quality informa- than that for slippers with clog thongs, leather- tion to the cerebral cortex. That causes shortening soled sandals and Japanese socks. The sole of the of the latency. In the same process, the strength of foot is covered with hairless skin and it is well- slippers without clog thongs increased compared known, like the palm of the hand, for being one of with that for slippers with clog thongs, leather- the most sensitive parts of the body, having a large soled sandals and Japanese socks. That shows that number of mechanoreceptors, nerve endings which differences caused by the existence of clog thongs recognize the dynamic changes of receptors or cells emerged in the information input function of the near receptors. Mechanoreceptors are nervous in- centripetality from the foot to higher central nerves put afferent devices which change information such as well as the efferent process of the joint control as static or dynamic conditions, balance, unbalance from the higher central nerves to the muscles. The and distortions into nerve-transmitted signals. unique function of the foot is the grabbing func- Those in the sole are intensified in the forefoot part tion. When human beings put their weight onto and in the heel, where most weight is applied. On the feet, and then try to move their bodies forward the basis of location, size and number, the Meissner or lose their balance unexpectedly, toes will 51 reflevely grab the ground. By keeping the toes people, physical therapists require knowledge and apart, it seems that the grabbing function to pertur- technologies from various fields such as neurology, bations is reinforced and the necessary strength for kinematics and vital dynamics of postural control. postural recovery relatively decreased. Next, the In other words, the field of fall prevention for eld- comparison among footwear types with clog thongs. erly people will be a good place for physical The latencies of slippers with clog thongs and therapists to make the best use of their knowledge leather-soled sandals were extended compared with and the development of footwear will be the most these for Japanese socks. It can be said that the important subject for physical therapists. delay of responses was caused because the informa- tion from the ground was absorbed and dispersed by REFERENCES the flexibility of the sole and the amount of informa- tion input from the sole was decreased. 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